The present invention is related to the field of governing functions of engine controllers.
Internal combustion engines may be operated in any one of several modes including user controlled, torque governed, and speed governed. User control is the most common mode where the user operates a foot pedal to request an amount of torque that the engine will generate. Increasing the requested torque generally causes an increase in the speed of the engine. User control relies upon the user to adjust the requested torque to account for variations in the loading upon the engine.
Torque governing is often used in conjunction with the user control to limit the amount of torque that the user may request of the engine. For example, it is desirable to limit the amount of torque an engine may produce to match the characteristics of an associated transmission. Torque limiting may be a simple maximum limit at all speeds, or vary as a function of the engine speed. Here, the idea is to avoid supplying more torque into the transmission or load than the transmission or load can handle. As the load on the engine increases, the engine speed is allowed to decrease under torque governing to avoid exceeding the maximum torque limit. As the load decreases, the engine speed is allowed to increase, again within the maximum speed and torque limits imposed by the governors.
Speed governing is used in situations where the speed of the engine must remain a constant despite a changing load condition. Examples of such applications include alternating current electrical generators where the frequency of the alternating current is dependent upon the engine speed. In this example, as the load on the generator increases, the torque produced by the engine must increase in order to maintain the constant engine speed, and thus a constant generator output frequency. The desired speed of the engine is controllable through a speed request signal input into the speed governor.
Many engine applications require the engine to operate in one or more of these modes at different times, and sometimes simultaneously. For example, a self-propelled highway-compatible crane operates in the torque governing mode when traveling on the highways. Once at a job site, the crane""s engine is operated in the speed governing mode for proper operation of the crane. When returning to highway travel, the user requires a convenient and reliable mechanism that insures that the speed governing mode is disabled and that the torque governing mode is enabled. One method currently in use to disable speed governing is to set the speed request signal to an out-of-range value. The speed governor will not control the engine speed without a valid speed request signal input. A drawback to this approach is that the speed governor may flag the out-of-range speed request signal as a failure. The users must either be taught to ignore this failure, or the diagnostics for this type of failure must be disabled. What is desired is an approach where the speed governor can be easily enabled and disabled while still accepting a valid speed request signal.
The present invention is an engine controller capable of operating in both a torque governing mode and a speed governing mode simultaneously, and a method of operation whereby speed governing may be enabled and disabled while simultaneously providing a valid speed request signal to the controller. A speed governor signal having an enabled state and a disabled state is generated external to the controller and monitored by the speed governor. A speed request signal is simultaneously monitored by the speed governor. The speed governor is operative to control the speed of the engine proportional to the to speed request signal while the speed governor signal is in the enabled state. The speed governor is disabled by setting the speed governor signal into the disabled state. A torque governor may also be operational within the controller. The torque governor monitors a torque request signal which it uses to control a torque generated by the engine.
In alternative embodiments, the speed governor is disabled when the speed request signal is out-of-range, either in excess of a high speed threshold, or below a low speed threshold. Likewise, the speed governor may be disabled when the torque request signal exceeds a high torque threshold indicating that the user wishes to override the speed governor and increase the engine""s torque production.
Transitioning the speed governor from disabled to enabled may also be dependent upon the speed request signal and/or torque request signal. In alternative embodiments, speed governor enablement may be restricted to occur only when the speed request signal is below an initial speed threshold to avoid a large sudden step in the requested speed. Likewise, speed governing enablement may by restricted to occur only when the torque request signal is below an initial torque threshold.
Accordingly, it is an object of the present invention to provide an engine controller and a method of operation whereby a speed governor of the controller can be easily enabled and disabled while maintaining a valid speed request signal.
These and other objects, features and advantages will be readily apparent upon consideration of the following detailed description in conjunction with the accompanying drawings.